Polymer saturated backing material



United States Patent Ofltice 3,296,022 Patented Jan. 3, 1967 The present invention relates in general to an improved saturant for fibrous webs and more particularly to such a saturant and b-ackings made therewith for use as a component of a coated abrasive product.

Fibrous webs, including among others, woven webs and non-woven webs, such as paper or the like, have commonly been impregnated with various saturants to vary the properties of such webs as desired for the end use in which these webs are a component. One area of use which has been known for many years is the coated abrasive field wherein the webs are used as backings to support a layer of abrasive grains adhesively secured to the web by a hard, rigid binder adhesive. Backings for this use must be capable of withstanding severe strain without tearing or ply separation and hence the use of saturants of various kinds has long been practiced for these products.

It is an object of the present invention to provide an improved saturant for fibrous webs.

A further object of the present invention is the provision of a high strength backing especially adapted to serve as a component of a coated abrasive product.

Additional objects, if not specifically set forth herein, will be readily apparent to one skilled in the art from the following detailed description of the invent-ion:

Generally, the present invention comprises the use, as a saturant or impre-gnant for fibrous webs, of a nylonphenolic resin blend. Small amounts of this saturant have been found to materially strengthen and improve both woven and non-woven fibrous webs, particularly for use as a coated abrasive backing component.

More specifically, the invention contemplates the use as a saturant of a blend of alcohol-soluble nylon with a thermosetting, alkali-catalyzed unmodified phenol-formaldehyde resin. The ratio of nylon to phenolic may range from 6.33:1 to 1:1 and the amount applied will vary, depending on the properties desired and the type of web treated, e.g., 25% to 50% by weight for a woven backing down to 1% or 2% by weight for some paper backings.

The alcohol-soluble nylons useful in this invention are those having the functional group:

wherein R is the organic radical derived from the alcohol used in forming the functional group as describe-d in United States Letters Patent No. 2,430,923 to Foster et a1.

Whereas methyl alcohol is most frequently used and hence there is there-by introduced an organic radical having one carbon atom, alcohols which introduce radicals having a greater number of carbon atoms may be used as, for example, ethanol, propanol, isopropanol and butanol. If a mixed alkoxymethyl derivative is desired, a mixture of alcohols can be used or different alcohols may be added at different stages of the manufacture of the alcohol-soluble nylon. The N-alkoxymethyl nylons -or filament-forming polyamides used in this invention preferably have a dilution value of 33 or more when the dilution value is determined by the method disclosed in the aforementioned Foster et al. patent (column 3, lines 25-39) but it has been found that the intrinsic viscosity as hereinafter defined is a better and more generally applicable guide than dilution values in the selection of nylons or filament-forming polyamides for use in the present invention. While suitable nylons for use in this invention are commercially available from E. I. du Pont de Nemours & Company, Wilmington, Delaware, U.S.A., such nylons may be prepared as illustrated in the following specific example:

Example 1 Three parts of formic acid (sp.gr.=1.2) is charged into a glass resin reaction flask equipped with a stirrer, 1 part nylon marquisette (polyhexamethylene adipamide) cut in very small pieces is added, the mixture is heated to 60 C. and solution is complete within 60 minutes. A second solution consisting of 0.933 part of paraformaldehyde aldehyde), 1 part of methanol and 0.0006 part of sodium hydroxide is prepared at 60 C. in an open glass beaker and 0.5 part of methyl formate is added. This second solution is added to the polyamide solution over a 3 /2 minute period with good agitation. The reaction mixture is maintained at 60 C., and 8 minutes after all the aldehyde solution has been added 1 part of second-stage methanol is added to the reaction mixture. Seventeen minutes later (25 minutes after all the aldehyde solution has been added) 2 parts of thirdstage methanol is added and 5 minutes later the reaction mixture is discharged into a precipitation vessel containing 28 parts of cold aqueous acetone (44% acetone by weight). The resulting solution is stirred vigorously and net-uralized with aqueous ammonia. The product, N-methoxymethyl polyhexamethylene adipamide, precipitates in finely divided, free-settling, granular form. It is separated from the mother liquor by decantation and washed by reslurrying with water. The decanted precipitate is dried in a vacuum at 50 C.

Instead of polyhexamethylene adipamide, other polyamides such as polyhexamethylene sebacamide or those derived from epsilon-aminocaproic acid, which are readily available commercially, may be used.

Some interpolymer nylons or filament-forming interpolyamides are well adapted for use in the present invention. Interpolymer nylons or filament-forming interpolyamides used in carrying out this invention are limited to those having suitable intrinsic viscosities and are the reaction product of at least three polyamide-forming reactants of which (a) one is a diprimary diamine containing at least 6, but not more than 14, carbon atoms; (b) one is a dibasic carboxylic acid containing at least 6, but not more than 12, carbon atoms; and (0) one is polyamide-forming material composed of at least one additional reactant different from the two others selected as defined in (a) and (b), which third reactant is, however, selected from other diprimary diamines defined in (a), or other dibasic carboxylic acids defined in (b), or from the polmerizable amino acids or from mixtures of two or more of such different diprimary diamines, such different acids and said amino acids.

The N-alkoxymethyl polyamides and the interpolyamides and mixture of the former and the latter suitable for use in the present invention have an intrinsic viscosity of 0.4 or more.

Intrinsic viscosity V(int.) for purposes of this invention, and in accordance with the practice of those skilled in the art, is the limit as 0 goes to 0 of V(sp.)/c wherein c is the concentration and wherein V(sp.) is the specific viscosity and is given by the equation:

fiow time of solution-flow time of solvent flow time of solvent of V(sp./c) at zero concentration is the intrinsic viscosity as the term is used herein.

Methods of measuring the intrinsic viscosity are well known in the art and the following procedure has been used with success:

The polyamides in the form of small /s" x A5") cubes are weighed out to 0.1 mg. as 0.35, 0.5 and 0.75 gram samples and transferred to glass-st'oppered bottles, to each of which exactly 100ml. of 80% formic acid was added. Several hours were required for solution to become complete, and in some instances the solutions were allowed to stand overnight at room temperature.

Into an Ostwald-Fenske viscometer having a capillary bore of 0.6 mm., 6.4 ml. of solution was added by pipette, the viscometer placed in a constant temperature bath at 25i0.05 C. and the apparatus allowed to come to equilibrium. Flow times were measured to 0.1 second 'by means of a stopwatch in the usual manner, and the average of at least three readings was used in the calcula tions. The flow time of the solvent was likewise determined under the same conditions.

The resin used in the saturant of the present invention is, as aforesaid, a thermosettin-g, alkali-catalyzed resin made from unsubstituted phenol. The ratio of formaldehyde to phenol may vary from 0.95:1 up to 2: 1, with the prefered ratio being 1.7:1.

The saturant of the present invention may be applied in any of the ways known to the art and the manner of such application does not form a part of the invention. The following examples illustrate the improvement in tear strength of paper treated with the saturant and also show the formation of a coated abrasive product from a fabric treated with the saturant:

Example 2 A standard wood pulp cylinder paper (130 #/papermakers ream) was tested for tear strength without any saturant added and the Elmendorf Tear Strength was found to be 350 gm. cm. Normally, the addition of any curing type saturant to such a paper would reduce the tear strength after cure to below that of the untreated paper. In this case the paper was impregnated with 2% by weight of a methanol solution containing 72% nylon solids and 28% phenolic resin solids. Curing the treated paper for one hour at varying temperatures produced the following tear strengths as measured on the Elmendorf Tear Testing Machine:

Cure, 1 hr. .at- Tear strength (gm. cm.)

300" F. 400 275 F. 448 250 F. 592

It will be noted that in all instances some improvement over the untreated paper was found to have occurred, but that at the 250 F. temperature the improvement in tear strength was approximately 70% As indicated, there was only about 2% by weight of the saturant added to achieve this drastic increase in tear strength.

Example 3 An abrasive belt was formed using as a backing an endless cotton :belt. The fabric used in the backing was a plain Weave cotton having a 38 x 30, 1 x 1 construction and weighing 23.2 pounds per ream. The 'belt was first pre-saturated by passing the same through a two-roll padder and a dip and squeeze with a 2% solution of the nylon-phenolic saturant described below. Saturation of the belt was then canried out by doctoring onto the belt a 28% solution of the saturant, preferably in three applications, to give a total pick-up of 34% saturant based on the weight of the fabric backing. The saturant was a 20% solution of nylon 66 (alcohol-soluble) in methanol mixed with a 75% solids solution of an unmodified phenolformaldehyde resin having a formaldehydezphenol ratio of 1.7:1.. Ninety parts of the nylon solution was added to 10 parts of the phenolic solution and the resin thoroughly dispersed in the nylon. After saturation, the fabric was dried for one-half hour at 160 F. The fabric then contained 6.9 p-ounds/ sandpaper ream of the saturant.

A backsize of a slurry of pelletized graphite and phenolic resin in denatured alcohol (55 parts phenolic to 45 parts graphite to 15 parts .alcohol) was then app-lied by a doctor knife to the saturated cloth in an amount of approximately 40% by we ght of the original cloth weight. The backsize was then dried and cured for about one hour at 250 F.

The material treated as above was in the form of an endless belt, 4" wide by 75" long. It was next slit to the desired widthin this case, As" x 75". The maker adhesive consisting of a phenolic resin adhesive was then applied to the surface of the belt and a blend of 35 parts diamonds and 65 parts flint .abrasive (both mesh) was applied uniformly to the adhesive. The total weight of grain was 0.63 gram. This product was then heated in step-wise fashion, with the maximum temperature reach- I ing 255 F., to set the maker adhesive, whereupon a size adhesive of a phenol-formaldehyde resin was applied over the abrasive, with a top cure of about one hour at 300 F. The finished belt was found to be capable both of polishing tungsten carbide and also of removing stock in a cutting operation. The diamond-flint abrasive referred to above is described in detail in our co-pending application, Serial No. 211,770, filed July 23, 1962.

By the term alcohol-soluble nylon as used herein and in the appended claims, is meant a polyamide as described herein which is soluble in hot methanol or hot ethanol.

In addition to increasing the tear strength of backings treated with the saturant of the present invention, it has been found that coated abrasives made on paper treated with such saturant have a tendency towards decreased curl-a definite advantage for this end use. Also, the saturant provides a waterproofing effect on cloth, fibre and paper backings.

By the term alkali-catalyzed" resin as used herein is meant not only resins catalyzed by a true alkali such as NaOH but also those resins catalyzed by materials having an alkaline pH such as the carbonates, amines, etc.

Obviously, many variations may be made without departing from the spirit and scope of the invention as described herein and therefore only such limitations as are contained in the appended claims should be imposed.

We claim:

1. A flexible backing for coated abrasives which comprises:

(a) A fibrous web; and

(b) A saturant for said web present in an amount of at least 1% by weight of said web;

(0) Said saturant comprising the reaction product of an alcohol-soluble nylon having a dilution value of at least 33 and an intrinsic viscosity of at least 0.4 with a thermosetting, alkali-catalyzed, unsubstituted phenolic resin;

((1) Said reaction product having a nylon to phenolic nesin ratio of from 6.33:1 to 1:1.

2. A flexible backing for coated abrasives which comprises:

(a) A fibrous web; and

(b) A saturant for said web present in an amount ranging from 1% to 50% :by weight of said web;

(c) Said saturant comprising the reaction product of an alcohol-soluble nylon having a dilution value of at least 33 and an intrinsic viscosity of at least 0.4 with a thermosettin-g, alkali-catalyzed, unsubstituted phenolic resin;

(d) Said reaction product having a nylon to phenolic resin ratio of from 6.33:1 to 1:1.

3. A flexible backing for coated abrasives which comprises:

(a) A fibrous web; and

(b) A saturant for said web present in an amount of at least 1% by weight of said web;

(c) Said saturant comprising the reaction product of an alcohol-soluble nylon having a "dilution value of at least 33 and an intrinsic viscosity of at least 0.4 with a thermosetting, alkali-catalyzed, unsubstituted phenolic resin having a formaldehyde to phenol ratio of from 0.95:1 to 2:1;

(d) Said reaction product having a nylon to phenolic resin ratio of from 6.33 to 1 to 1:1.

4. A flexible backing for coated abrasives which comprises:

(a) A fibrous web; and

(b) A saturant for said web present in an amount ranging from 1% to 50% by weight of said web;

(c) Said saturant comprising the reaction product of an alcohol-soluble nylon having a dilution value of at least 33 and an intrinsic viscosity of at least 0.4 with a thermosetting, alkali-catalyzed, unsubstituted References Cited by the Examiner UNITED STATES PATENTS Hanford 260-43 Watson et a1 26043 Beauchamp 260 -43 Ball 51-298.1 Works et a1. 260-43 WILLIAM D. MARTIN, Primary Examiner.

DONALD ELZAJA, Examiner.

J. J. KLOCKO, H. W. MYLIUS, Assistant Examiners. 

1. A FLEXIBLE BACKING FOR COATED ABRASIVES WHICH COMPRISES: (A) A FRIBROUS WEB; AND (B) A SATURANT FOR SAID WEB PRESENT IN AN AMOUNT OF AT LEAST 1% BY WEIGHT OF SAID WEB; (C) SAID SATURANT COMPRISING THE REACTION PRODUCT OF AN ALCOHOL-SOLUBLE NYLON HAVING A DILUTION VALUE OF AT LEAST 33 AND AN INTRINSIC VISCOSITY OF AT LEAST 0.4 WITH A THERMOSETTING, ALKYL-CATALYZED, UNSUBSTITUTED PHENOLIC RESIN; (D) SAID REACTION PRODUCT HAVING A NYLON TO PHENOLIC RESIN RATIO OF FROM 6.33:1 TO 1:1. 